Transfer of fixation between targets at different viewing distances involves changes in vergence eye movements and accommodation that operate to eliminate disparity and blur, respectively. During monocular viewing, when disparity cues are absent, changes in accommodation due to blur also result in linear changes in vergence: the accommodation-vergence response. The present experiments were undertaken to determine whether these open-loop responses are subject to visually-mediated adaptive regulation. Human subjects were fitted with specially made laterally-displacing periscopic spectacles to increase the apparent separation of the two eyes and thereby increase the required change in convergence per unit change in accommodation necessary to maintain single, clear vision. Thirty minutes of exposure to these spectacles was enough to cause large increases in the vergence change associated with a unit change in accommodation during monocular testing. This finding supports the view that the close coupling between vergence and accommodation is subject to adaptive regulation. Decreasing the apparent separation of the eyes with medially-displacing (cyclopean) spectacles failed to affect the magnitude of the accommodation-vergence response. Thus, the adaptive mechanism shows considerable asymmetry.